Quoridor is nice but I would not even put it in the top 10 modern abstracts, let alone on par with chess.
Legality aside, it is a bit of a dick move to reimplement a modern abstract that people can play for free, or even make themselves for a low cost, just because you don't like the (free) site it's on.
Bga has fixed set of features for all its games. And their focus is divided.
This game atleast deserves its own home.
But I think your ignorance of the hobbyist game market is revealed a bit here already (not having full context for BGA, not knowing if Gigamic still owns it - they certainly do and had a booth at Essen this year like they do every year) - and you're vastly overestimating not just Quoridor's popularity but the size of the entire market for non-chess/go/tables/poker games. And I don't just mean financially - dozens of variants are no good if there are barely enough players to match dozens of games to begin with.
Did you try contacting BGA to see if you could get the Studio files for Quoridor?
[1] Popular within the modern board game community, at least.
Also BGA is pretty big and large. It's already one of the best places to put digital implementations of games, and that's why you see major hobby games come out on there, like Wingspan and Ark Nova, with about 75 or more new games added to the site every year, including games that haven't even been released yet and still on Kickstarter, like Undergrove recently.
And yeah, I've bought probably at least a dozen games now after playing them on BGA first. It's fun to play them on BGA, but I'd also like to play them in person with my friends, too.